Tumour pseudoresponse

Tumour pseudoresponse, also known just as pseudoresponse, refers to the phenomenon of tumours appearing to respond to a specific treatment on imaging criteria, when the lesion actually remains stable or has even progressed.

The term is largely used in brain tumours imaging follow-up, especially for high grade gliomas (e.g. glioblastoma) in which a rapid decrease in contrast enhancement and oedema can be observed in a short period of time after administration of antiangiogenic agents (e.g, bevacizumab and cediranib), often without any significative change in actual tumour size (as visualised by T2 (non-enhancing tumour) or diffusion / perfusion studies 1-3.

Bevacizumab (trade name Avastin) for example, is an inhibitor of vascular endothelial growth factor (VEGF), aimed at inhibiting the formation of new blood vessels within the tumour (neoangiogenesis). VEGF is produced by the tumours, and not only promotes neoangiogenesis but also reduces effectiveness of gap junction and creates fenestrations in the endothelium of existing brain capillaries, leading to oedema and enhancement 4. The amount of VEGF produced has been shown to correlate with tumour grade.

The changes seen in pseudoresponse (rapid reduction in enhancement and vasogenic oedema) are largely mediated by changes in blood brain barrier permeability rather than antiangiogenic effects, meaning that relying on enhancement and T2 signal change can be misleading when interpreting follow up MRI studies 4.

Despite the fact that these advanced MRI sequences have helped in differentiating pseudoresponse from a true response, imaging follow-up is still required 1. Essential to correct interpretation is the availability of multiple previous imaging studies and information relating to type and timing of therapy.